Core unit C (Flow Cytometry and Cell Sorting) will be responsible for the analysis and sorting of hemopoietic stem cells, committed progenitor cells and other hemopoietic cells with different degrees of maturation and developmental differentiation by flow cytometric procedures. The unit will interact with the investigators of the SCOR projects to provide them with optimal scientific and technical support to study the onset and regulation of the expression of the various blood group antigens. For this purpose the unit will provide technical support to the SCOR project by: 1) analyzing and sorting subpopulations of bone marrow and cord blood using antibodies against CD34, kit ligand, glycophorin and transferrin receptor, anti-Rh 29 antibody B10, as well as the dyes Rhodamine 123 and Hoechst 33342. Control cells, such as well defined subpopulations from non-erythroid differentiation lineages, will also be sorted. The sorted cells will be prepared for the investigators of the SCOR project for further molecular and functional analysis; 2) studying the expression and the presence of blood group antigens on stem cell fractions using RT-PCR and three-color immunofluorescence techniques; 3) analyzing and screening newly developed monoclonal antibodies with regard to their specificity for blood group antigens; and, 4) combining the antibodies which become available because of this SCOR project with each other and with anti-glycophorin and anti-transferrin receptor antibodies to sort well defined intermediate stages of erythroid differentiation.